The general aim of our research program is to increase our understanding of the structure and assembly of Rous sarcoma virus (RSV), an avian retrovirus. This work will complement the structural work on Human immunodeficiency virus (HIV) carried out in this and other laboratories over the past few years. In the mature retrovirus, the retroviral capsid protein forms a shell, which encapsidates the viral RNA. The morphology of this core structure is dramatically different for different retroviruses. Nevertheless it seems likely that there are fundamental similarities in the organization of all retroviral cores. We aim to address this question by structural studies on the RSV capsid protein. From this and other studies we can begin to understand capsidcapsid interactions, and how they might determine core assembly and morphology.